1. Field of Invention
The present invention relates to a method of correcting clutch characteristics of a vehicle, and more particularly, to a technology for correcting variation characteristics of the transmission torque of a clutch depending on the stroke of an actuator considering the difference in temperature between the surface and the core part of the clutch.
2. Description of Related Art
Semi-automatic transmissions, such as automated manual transmissions (AMTs) and double clutch transmissions (DCTs), are systems which automatically control a manual transmission mechanism. Unlike typical automatic transmissions (ATs) which use a torque converter and a wet multi-plate clutch, semi-automatic transmissions are frequently configured such that they use a dry clutch to transmit engine torque to a transmission mechanism.
The dry clutch is controlled by an actuator. In general, the actuator is controlled based on a torque-stroke (T-S) curve that presents variations in the transmission torque of the dry clutch with respect to the stroke of the actuator.
The dry clutch is characterized in that the transmission torque thereof significantly varies depending on a variety of factors, such as a single part tolerance of each component, a degree of wear due to the progression of duration, thermal deformation at high temperature and a variation in the coefficient of friction of a disk. It is difficult to convert the transmission torque of the dry clutch into a preset form of data.
However, the dry clutch fails to properly reflect variations in the characteristics of the transmission torque when controlling the actuator. When the actuator is controlled insufficiently or excessively, the dry clutch may slip excessively or be subjected to an impact. There is required a technique for accurately finding transmission torque characteristics of the dry clutch depending on the actuator stroke so as to be used in control over the actuator.
FIGS. 1 and 2 are graphs showing variations in a T-S curve depending on changes in temperature of two clutches, i.e. a first clutch and a second clutch, which are used in a DCT. Here, FIG. 1 shows the transmission torque characteristics of the first clutch. Referring to the graph of the first clutch in FIG. 1, the T-S curve moves to the right depending on a rise in the temperature, leading to a situation in which more actuator strokes are required in order to produce the same clutch transmission torque. At a preset temperature or higher, the T-S curve moves to the left, leading to a situation in which the same clutch transmission torque can be produced from fewer actuator stroke.
FIG. 2 shows the transmission torque characteristics of a second clutch. Referring to FIG. 2, the T-S curve tends to move to the left depending on a rise in the temperature. It can be estimated that the different transmission torque characteristics of the first clutch and the second clutch are caused by the positions and shapes of respective clutches.
In the control over the clutch using the T-S curve as described above, a representative temperature value is estimated on the assumption that the temperature of the clutch is uniform over the entire clutch, a T-S curve is selected based on the estimated representative temperature value, and thus an actuator stroke for producing an intended clutch transmission torque is determined.
However, in fact, the temperature of the surface of the clutch practically differs from the temperature of the core of the clutch. When heat is heavily generated due to the slipping of the clutch since a gear-changing time is prolonged as in kick-down gear change, the difference in the temperature between the surface and the core of the clutch is significantly increased. If the T-S curve is selected based on one representative temperature value as above by disregarding such a difference and the actuator stroke is determined using the T-S curve, an intended clutch transmission torque is not produced. This improper situation causes the clutch to excessively slip or be impacted.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.